package java.security.cert;

import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidParameterException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.util.Set;

/**
 * Parameters used as input for the PKIX <code>CertPathBuilder</code> 
 * algorithm.<br />
 * <br />
 * A PKIX <code>CertPathBuilder</code> uses these parameters to {@link 
 * CertPathBuilder#build build} a <code>CertPath</code> which has been 
 * validated according to the PKIX certification path validation algorithm.<br />
 * <br />
 * To instantiate a <code>PKIXBuilderParameters</code> object, an
 * application must specify one or more <i>most-trusted CAs</i> as defined by
 * the PKIX certification path validation algorithm. The most-trusted CA 
 * can be specified using one of two constructors. An application 
 * can call {@link #PKIXBuilderParameters(Set, CertSelector) 
 * PKIXBuilderParameters(Set, CertSelector)}, specifying a 
 * <code>Set</code> of <code>TrustAnchor</code> objects, each of which 
 * identifies a most-trusted CA. Alternatively, an application can call 
 * {@link #PKIXBuilderParameters(KeyStore, CertSelector)
 * PKIXBuilderParameters(KeyStore, CertSelector)}, specifying a 
 * <code>KeyStore</code> instance containing trusted certificate entries, each 
 * of which will be considered as a most-trusted CA.<br />
 * <br />
 * In addition, an application must specify constraints on the target 
 * certificate that the <code>CertPathBuilder</code> will attempt 
 * to build a path to. The constraints are specified as a 
 * <code>CertSelector</code> object. These constraints should provide the 
 * <code>CertPathBuilder</code> with enough search criteria to find the target 
 * certificate. Minimal criteria for an <code>X509Certificate</code> usually 
 * include the subject name and/or one or more subject alternative names.
 * If enough criteria is not specified, the <code>CertPathBuilder</code> 
 * may throw a <code>CertPathBuilderException</code>.<br />
 * <br />
 * <b>Concurrent Access</b><br />
 * <br />
 * Unless otherwise specified, the methods defined in this class are not
 * thread-safe. Multiple threads that need to access a single
 * object concurrently should synchronize amongst themselves and
 * provide the necessary locking. Multiple threads each manipulating
 * separate objects need not synchronize.
 *
 * @see CertPathBuilder
 **/
public class PKIXBuilderParameters extends PKIXParameters
{
    private int maxPathLength = 5;

	/**
	 * Creates an instance of <code>PKIXBuilderParameters</code> with
	 * the specified <code>Set</code> of most-trusted CAs. 
	 * Each element of the set is a {@link TrustAnchor TrustAnchor}.<br />
	 * <br />
	 * Note that the <code>Set</code> is copied to protect against
	 * subsequent modifications.
	 *
	 * @param trustAnchors a <code>Set</code> of <code>TrustAnchor</code>s
	 * @param targetConstraints a <code>CertSelector</code> specifying the 
	 * constraints on the target certificate 
	 *
	 * @exception InvalidAlgorithmParameterException if <code>trustAnchors</code> 
	 * is empty <code>(trustAnchors.isEmpty() == true)</code>
	 * @exception NullPointerException if <code>trustAnchors</code> is 
	 * <code>null</code>
	 * @exception ClassCastException if any of the elements of
	 * <code>trustAnchors</code> are not of type 
	 * <code>java.security.cert.TrustAnchor</code>
	 */
    public PKIXBuilderParameters(
		Set trustAnchors,
		CertSelector targetConstraints)
	throws InvalidAlgorithmParameterException
    {
	super( trustAnchors );
	setTargetCertConstraints( targetConstraints );
    }

	/**
	 * Creates an instance of <code>PKIXBuilderParameters</code> that
	 * populates the set of most-trusted CAs from the trusted
	 * certificate entries contained in the specified <code>KeyStore</code>.
	 * Only keystore entries that contain trusted <code>X509Certificate</code>s
	 * are considered; all other certificate types are ignored.
	 *
	 * @param keystore a <code>KeyStore</code> from which the set of 
	 * most-trusted CAs will be populated
	 * @param targetConstraints a <code>CertSelector</code> specifying the 
	 * constraints on the target certificate 
	 *
	 * @exception KeyStoreException if <code>keystore</code> has not been 
	 * initialized
	 * @exception InvalidAlgorithmParameterException if <code>keystore</code> does
	 * not contain at least one trusted certificate entry
	 * @exception NullPointerException if <code>keystore</code> is 
	 * <code>null</code>
	 */
    public PKIXBuilderParameters(KeyStore keystore,
				 CertSelector targetConstraints)
	throws KeyStoreException,
	InvalidAlgorithmParameterException
    {
	super( keystore );
	setTargetCertConstraints( targetConstraints );
    }

	/**
	 * Sets the value of the maximum number of non-self-issued intermediate
	 * certificates that may exist in a certification path. A certificate
	 * is self-issued if the DNs that appear in the subject and issuer
	 * fields are identical and are not empty. Note that the last certificate
	 * in a certification path is not an intermediate certificate, and is not
	 * included in this limit. Usually the last certificate is an end entity
	 * certificate, but it can be a CA certificate. A PKIX 
	 * <code>CertPathBuilder</code> instance must not build 
	 * paths longer than the length specified.<br />
	 * <br />
	 * A value of 0 implies that the path can only contain
	 * a single certificate. A value of -1 implies that the
	 * path length is unconstrained (i.e. there is no maximum).
	 * The default maximum path length, if not specified, is 5.
	 * Setting a value less than -1 will cause an exception to be thrown.<br />
	 * <br />
	 * If any of the CA certificates contain the 
	 * <code>BasicConstraintsExtension</code>, the value of the
	 * <code>pathLenConstraint</code> field of the extension overrides
	 * the maximum path length parameter whenever the result is a
	 * certification path of smaller length.
	 *
	 * @param maxPathLength the maximum number of non-self-issued intermediate
	 *  certificates that may exist in a certification path
	 *
	 * @exception InvalidParameterException if <code>maxPathLength</code> is set 
	 *  to a value less than -1
	 *
	 * @see #getMaxPathLength
	 */
    public void setMaxPathLength(int maxPathLength)
    {
	if ( maxPathLength < -1 )
	    throw new InvalidParameterException("the maximum path length parameter can not be less than -1");
	this.maxPathLength = maxPathLength;
    }

	/**
	 * Returns the value of the maximum number of intermediate non-self-issued
	 * certificates that may exist in a certification path. See
	 * the {@link #setMaxPathLength} method for more details.
	 *
	 * @return the maximum number of non-self-issued intermediate certificates 
	 *  that may exist in a certification path, or -1 if there is no limit
	 *
	 * @see #setMaxPathLength
	 */
    public int getMaxPathLength()
    {
	return maxPathLength;
    }

	/**
	 * Returns a formatted string describing the parameters.
	 *
	 * @return a formatted string describing the parameters
	 */
    public String toString()
    {
	StringBuffer s = new StringBuffer();
	s.append( "PKIXBuilderParameters [\n" );
	s.append( super.toString() );
	s.append( "  Maximum Path Length: " );
	s.append( getMaxPathLength() );
	s.append( "\n]\n" );
	return s.toString();
    }
}
